1. The Field of the Invention
The present invention relates to gas filter systems used with fluid processing systems and methods for using such gas filter systems.
2. The Relevant Technology
Bioreactors are used in the growth of cells and microorganisms. A typical bioreactor includes a container which holds a suspension comprised of liquid growth media, a culture of cells or microorganisms, and other desired nutrients and components. A rotatable impeller is operated within the suspension to maintain the suspension in a substantially homogenous state. Small gas bubbles are continuously sparged into the suspension and are typically used to help oxygenate the culture, strip out unwanted CO2 from the suspension and control the pH of the suspension.
To maintain the viability of the culture, the compartment in which the culture is being grown must remain sterile. To remove the sparged gas that is being continuously added to the suspension while maintaining sterility of the compartment, the gas is typically removed through a filter system. One conventional filter system is referred to as a cartridge filter system and includes a rigid, metal housing into which a cartridge filter is removably positioned. Gas from the container is delivered to an inlet on the housing. The gas then travels through the filter within the housing and is then expelled to the environment through an outlet on the housing. The filter prevents any biological matter within the container from being expelled into the environment and prevents any contaminates in the environment from entering into the container.
Although useful, the conventional cartridge filter system has a number of shortcomings. For example, the metal housing in which the cartridge filter is placed is time consuming and labor intensive to maintain because it must be cleaned and sterilized between each use. Cleaning the metal housing can introduce chemical contaminants and leave production residuals. Furthermore, in addition to being expensive to purchase, the metal housing is cumbersome, both because it is a stand-alone item that occupies substantial space around the bioreactor and because it requires a relatively long length of tubing that must be run from the container and then sterilely connected to the housing. In addition, because the filter slowly clogs during use, the problems are compounded because multiple filter housings must be connected in parallel to ensure that the process can be continuously operated until the culture is fully grown.
In one attempt to address some of the above shortcomings, capsule filters have also been used with bioreactors. A capsule filter comprises a rigid plastic housing that permanently encases a filter. Although capsule filters are disposable and thus do not need to be cleaned or sterilized, they have their own drawbacks. For example, capsule filters are designed to be capable of operating at relatively high pressures and are typically rated for about 500 kPa. To enable operation at this pressure, the plastic housing is required to be relatively thick, thereby increasing the expense to the filter and making it relatively large and bulky. Furthermore, the capsule filters have a relatively small inlet and outlet port through which the gas travels. As a result of the small diameter ports, if a large gas flow rate is being processed, the system must either be operated at a high gas pressure, which can be undesirable in some circumstances, or multiple filters must be used, which increases cost and complexity.
The sparge gas passing through the suspension will carry moisture toward the filter assembly. Moisture that condenses on the filters will clog the filters. To limit the rate at which the filters are clogged, a condenser system can be placed between the reactor container and the filter system. The condenser system removes a portion of the moisture from the gas before it reaches the filter system. Traditional condenser systems, however, are often inconvenient to use in that they are typically complex, stand-alone systems that require multiple tubes that need sterile connections with the container and filter assembly. Furthermore, the condenser systems typically restrict the gas flow rate and thereby require that the system be operated at an elevated pressure. Condenser system can also be difficult to adjust for different gas flow rates.
Accordingly, what is needed in the art are condenser systems and filtration systems that can be used with bioreactors and other fluid processing systems that solve some or all of the above problems.